An emerging category of electronic devices is time-of-flight (TOF) systems. The TOF systems find applications in accelerometers, monolithic gyroscopes, light sensors, conveyor belts, depth sensing, proximity sensing, gesture recognition and imagers. A TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses. The target is any object of interest which may include, but not limited to, a human, an automated component, an animal, an electronic device etc. A TOF sensor in the TOF system receives the reflected light pulses. The TOF sensor receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system.
The TOF sensor includes a pixel array having a plurality of pixels. The pixel array receives the reflected light pulses. The pixel array collects light for a predetermined amount of time after the emission of the light by the light source. Light reflected from a far away object travels a longer distance and therefore has a longer time-of-flight, whereas light reflected from a nearby object is received after short time-of-flight. Each pixel in the pixel array generates a signal, which is processed in a processor to extract information about the target. The information includes a level of ambient light and a depth of the target.
The light source in a typical TOF system is a light emitting diode (LED) or a laser module. An illumination driver is required to drive the light source. The illumination driver needs to satisfy multiple conditions to be used in a TOF system. Some of these conditions are: (a) the illumination driver is required to support high current which in one example is in range of 100 mA or more, (b) the illumination driver is required to operate on high modulation frequencies which in one example is in the range of 50 MHz or more so as to achieve good depth accuracy, and (c) the illumination driver is required to have a good phase noise which in one example is of the order of 60-70 dB so as to achieve a good resolution.
Existing illumination drivers does not meet one or more of these conditions. In addition, the existing illumination drivers are affected by thermal noise, flicker noise and large sized circuit elements. The presence of parasitic capacitance further degrades a linear nature of the illumination drivers.